Ion reflectron comprising a flexible printed circuit board

ABSTRACT

A novel technique utilizing the precision of printed circuit board design and the physical versatility of thin, flexible substrates is disclosed to produce a new type of ion reflector. A precisely defined series of thin conductive strips (traces) are etched onto a flat, flexible circuit board substrate. Preferably, the thin conductive strips are further apart at one end of the substrate and get increasingly closer towards the other end of the substrate. The flexible substrate is then rolled into a tube to form the reflector body, with the conductive strips forming the rings of the ion reflector. The spacing between the traces, and hence the ring spacing, can be readily varied by adjusting the conductor pattern on the substrate sheet during the etching process. By adjusting the spacing between the rings, the characteristics of the field created by the reflectron can be easily customized to the needs of the user.

[0001] This application is a divisional of application Ser. No.09/639,145, filed on Aug. 16, 2000, the entire disclosure of which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a Time-of-Flight (TOF) massspectrometer and, more particularly, to a novel ion reflectron useablein, for example, a TOF mass spectrometer and a method of manufacturingsame.

[0004] 2. Description of the Related Art

[0005] A spectrometer is an analytical instrument in which an emission(e.g., particles or radiation) is dispersed according to some property(e.g., mass or energy) of the emission and the amount of dispersion ismeasured. Analysis of the dispersion measurement can reveal informationregarding the emission, such as the identity of the individual particlesof the emission.

[0006] It is well known that energy applied to ionized particles (ions)via an electric field will cause the ions to move. This principle isused in different kinds of spectrometers to accomplish different goals.For example, an ion mobility spectrometer (IMS) is used to detect andanalyze organic vapors or contaminants in the atmosphere. As describedand shown in U.S. Pat. No. 5,834,771 to Yoon et al, a typical IMSdetector cell (also called an ion drift tube) comprises a reactionregion for generating ions, a drift region or drift tube for separatingions, and a collector.

[0007] A carrier or drift gas along with a sample gas introduced intothe IMS are ionized and then the sample is moved through the drift tubeby an electric field applied along the drift tube. Different ions in thesample are separated based on their behavior in the drift tube as theycollide with the drift gas. Each type of ion exhibits its ownidentifiable behavior pattern based on its particular structure, e.g.,each ion shows unique velocity due to its mass, size, and charge. Theseparated ions proceed further down the drift tube and collide with thecollector, producing a measurable current. The drift velocities and thepeak currents of the ions arriving at the collector provide a basis forapproximating the identity of the samples introduced into the reactionregion; however, it is not an exacting technique, since two differention types having similar masses and similar interaction with the driftgas will be difficult, if not impossible, to distinguish from eachother.

[0008] A variety of methods of generating the electrical field used inthe reaction region and the drift tube are available, as described inthe previously-mentioned '771 patent. The subject matter of the '771patent is directed to one such method involving the fixation of aflexible printed circuit board onto the surface of the drift tube.Evenly-spaced parallel conductive bands are patterned on the flexiblecircuit board and the electrically conductive bands are connected toadjacent bands via resistances. Through proper biasing of the resistors,the conductive bands are placed at potentials relative to theirpositions along the tube, so that a uniform electric field is developedalong the axis of the tube.

[0009] Mass spectrometry is another well-known spectrometry method. Massspectrometers are used to determine, with precision, the chemicalcomposition of substances and the structures of molecules. One type ofmass spectrometer, a time-off-light (TOF) mass spectrometer, is aninstrument that records the mass spectra of compounds or mixtures ofcompounds by measuring the times (usually of the order of tens tohundreds of microseconds) for molecular and/or fragment ions of thosecompounds to traverse a (generally) field-free drift region within ahigh vacuum environment. TOF mass spectrometers operate based on theprinciple that, when ions are accelerated with a fixed energy, thevelocity of the ions differ dependant exclusively on mass and charge.Thus, the time-of-flight from point A to point B will likewise differdependant on the mass of the ion. Using a TOF mass spectrometer, themass of an ion can be calculated based upon its time of flight. Thereare no collisions with a carrier gas as occurs in an IMS—only thevelocity, and therefore the mass and charge (usually +1), is utilizedfor the calculation. This allows the molecule to be identified withprecision.

[0010] TOF mass spectrometers are comprised of a source region, whereneutral molecules are ionized, a drift region, followed by an ionreflector (also known as a reflectron) and a detector. In the ionsource, ions are formed in a high vacuum environment followed byacceleration down a field free drift region. The ions separate in timedependent only on their mass/charge ratio (normally the charge is +1).Upon entering the opposing field created by the ion reflector, ionsgradually slow down, stop, and reverse direction. The detection occursafter the ions are re-accelerated out of the ion reflector. In additionto enabling the calculation of the mass of the ions, ion packet peakwidths are sharpened by their passage through the ion reflector,resulting in an enhancement of the instrument's resolving power.

[0011] Reflectrons have been in use since the late 1960's and aretypically constructed by configuring plural individually manufacturedmetallic rings along ceramic rods using insulating spacers to separateeach ring from the next. This technique is labor intensive, costly, andlimits the flexibility of design due to the manufacture and handling ofextremely thin rings (a few mils in thickness) of relatively largediameter (1″ or greater). An example of such a configuration is shown inU.S. Pat. No. 4,625,112 to Yoshida,. While many permutations of thisdevice exist, the method of construction has been limited to the ringmethod described above.

[0012] Similar to the parallel conductive traces of the '771 patent, therings are placed at potentials that develop electric fields along theaxis of the cylinder. However, in contrast to the IMS method, whichdevelops a uniform electric field along the drift tube and which canonly approximate the identity of molecules in a sample, a TOF massspectrometer is capable of measuring atomic and molcular weights withhigh precision. Furthermore, to improve performance in a TOF massspectrometer, reflectrons have been constructed which developnon-uniform fields along the reflectron tube. The non-uniform fields aregenerated by utilizing a voltage divider network which varies thepotential applied to each of the evenly-spaced rings. A detailedexplanation of non-linear reflectron theory can be found in U.S. Pat.No. 5,464,985 to Cornish et al., incorporated fully herein by reference.

[0013] While the above-described TOF mass spectrometer design has provedquite satisfactory for large reflectors in which the rings arerelatively large in diameter and equally spaced, new applicationsutilizing remote TOF mass spectrometers may require miniaturizedcomponents, rugged construction, and/or the use of lightweightmaterials. Smaller TOF mass spectrometers have reduced drift length,necessitating the use of ideal energy focusing devices (reflectrons) tomaximize resolution.

[0014] Therefore, it would be desirable to develop new methods ofconstruction to fabricate miniature ion reflectors for TOF's which aresmaller, rugged, and lightweight and which provide maximum resolution.

SUMMARY OF THE INVENTION

[0015] To this end, a novel technique utilizing the precision of printedcircuit board design and the physical versatility of thin, flexiblesubstrates has been devised to produce a new type of ion reflector. Inthis method, a precisely defined series of thin conductive strips(traces) are etched onto a flat, flexible circuit board substrate. Theflexible substrate is then rolled into a tube to form the reflectorbody, with the conductive strips forming the rings of the ion reflector.The spacing between the traces, and hence the ring spacing, can bereadily varied by adjusting the conductor pattern on the substrate sheetduring the etching process.

[0016] The present invention is a multi-layered reflectron for atime-of-flight (TOF) mass spectrometer, comprising: plural structurallayers; and at least one flexible electrode layer, the flexibleelectrode layer creating an electric field in the reflectron when avoltage is applied thereto to slow down, stop, and reverse the directionof travel of ions traveling through said reflectron. The flexibleelectrode layer comprises a flexible substrate having a plurality ofconducting traces formed thereon, the flexible substrate being rolledinto a tubular shape so that said conducting traces form ringssurrounding a central axis through the length of the reflectron. Thedistance between the conducting traces, and therefore the rings, can, ifdesired, gradually decrease from one end of the reflectron to the other.The distance between the conducting traces can also be equally spaced,or user defined (any spacing desired).

[0017] The method of manufacturing a reflectron according to onerepresentation of the present invention can comprise the steps of:photo-etching a plurality of conducting traces onto a flexible substratesheet; wrapping the photo-etched substrate sheet around a mandrel sothat the plural conducting traces coincide to form a plurality of ringssurrounding the mandrel, leaving a connector end of the flexiblesubstrate sheet unwrapped; wrapping one or more plies or layers ofuncured, pre-impregnated composite material around the substrate, sothat all of the exposed portion of the substrate, except for theunwrapped connector end, is covered by the composite material ply(s);curing the photo-etched substrate and composite material on the mandrel;and removing the cured photo-etched substrate and composite materialfrom the mandrel to form a rigid tubular reflectron.

[0018] These objects, together with other objects and advantages whichwill be subsequently apparent, reside in the details of construction andoperation as more fully described and claimed hereinafter, referencebeing had to the accompanying drawings forming a part hereof, whereinlike reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 illustrates a flexible circuit board substrate preparedaccording to a first fabrication step of the present invention;

[0020]FIG. 2 illustrates a second fabrication step in accordance withthe present invention

[0021]FIG. 3 illustrates a third fabrication step in accordance with thepresent invention;

[0022]FIG. 4 illustrates a reflector assembly fabricated in accordancewith the steps illustrated in FIGS. 1-3;

[0023]FIG. 5 illustrates that a connector end of the flexible circuitboard of the present invention can be terminated at a rigid circuitportion; and

[0024]FIG. 6 illustrates that the flexible circuit board of the presentinvention can be split into multiple segments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]FIG. 1 illustrates a circuit board substrate 100 preparedaccording to a first step of the present invention. In accordance withthe present invention, parallel conductive traces 102 (50 traces areillustrated in FIG. 1 for purpose of example) are etched into theflexible circuit board substrate material using conventional etchingmethods. In the example shown in FIG. 1, a connector end 104 of theconducting traces 102 is etched such that the conducting traces 102 areangled at a tapered section 106. This allows the conducting traces 102to converge at connector end 104 so that at a connector section 108,they are closer together and properly aligned, thereby allowing for easyattachment of a connector (not shown).

[0026] In one representation of the present invention, the circuit boardsubstrate 100 comprises copper clad Kapton (manufactured by Dupont)polyimide film approximately 0.002″ thick, and the conductive traces 102etched onto the circuit board substrate 102 are approximately 0.008″wide by 0.001″ thick. The distance between each conductive trace can beuniform or, as shown in FIG. 1, can be narrower between some traces andwider between others. The distance between the rings in a reflectrontube affects the field generated by the tube, and thus the distancebetween the traces or the width of the traces can be adjusted accordingto the needs of the end-user. Further, as discussed in more detailbelow, traces A and B on either end (see FIG. 1) may be wider than theother traces to facilitate electrical connections to the outermost ringswhen fabrication of the reflectron is completed.

[0027] Once the flexible circuit board substrate 100 has been etched asdescribed above it is rolled into the shape of a tube and supported inthis tubular shape in a rigid fashion. While supporting the tube in arigid fashion is not required, doing so will assure symmetry of therings formed by the rolling of the flexible circuit board substrate 100,which results in precision with respect to the field generated by therings.

[0028] Referring now to FIGS. 2 and 3, given as examples. In FIG. 2, theflexible circuit board substrate 100 is rolled around a mandrel 210 toform the tubular shape. When the flexible circuit board substrate 100 isrolled around mandrel 210, each trace aligns with itself to form therings required to create the fields. Due to the thinness of the flexiblecircuit board 100, there is no need to electrically connect the ends ofeach trace; they are at the same potential assuring a continuous fieldinside the tube.

[0029] Next, layers of uncured, pre-impregnated fiberglass are wrappedaround the flexible circuit board substrate 100 which is wrapped aroundthe mandrel 210 (FIG. 3). In FIG. 3, five fiberglass plies 312, 314,316, 318, and 320, each approximately 0.010″ thick, are used. Thedimensions of the fiberglass plies should be such that their widthequals or exceeds the distance “W” of FIG. 1, and their length isapproximately equal to the circumference of the mandrel 210.

[0030] By using fiberglass plies having this length, when the plies arewrapped around the rolled flexible circuit board substrate 100, a slightopening 324 exists through which the connector end 104 of the flexiblecircuit board substrate 100 can extend. To allow the flexible circuitboard substrate 100 to follow its natural shape and thus minimizecreasing, in the second embodiment the starting position of eachsuccessive fiberglass ply is moved slightly with respect to the previousply so that a gradual “ramp” 326 is formed, thereby creating a gradualangling of the flexible substrate 100 away from the mandrel 210 asshown.

[0031] Once the reflector assembly is formed as described above, theassembly is cured under heat and pressure in a known manner forapproximately two hours. Then the assembly is allowed to cool and themandrel 210 is removed. It should be noted that other materials can beused that do not require curing with heat and pressure. Therefore, thetype of material used in the assembly dictates the type of curing. Thefinal wall thickness of the rolled reflector assembly constructed inthis manner is approximately 0.060″. A reflector assembly fabricatedaccording to the previously described steps is shown in FIG. 4. Astandard connector 430, such as a standard 50 pin ribbon connector maybe coupled to the connector end 104 so that the reflectron can be easilyincorporated into a mass spectrometer or any other device requiring areflectron. If desired, end caps, (e.g., polycarbonate plugs, not shown,or other suitable material) can be installed on either end of thereflectron to both support the reflectron in the vacuum chamber of themass spectrometer and to provide a surface on which to affix grids. Asis well known, the grids define and shape the field of the massspectrometer and are usually made of stainless or nickel and/or etchedwire electrically connected to traces A and B. The larger width oftraces A and B maximizes the integrity of the electrical connectionbetween the grid/caps and the traces. The cylindrical shape of thesupport tube and integral ring structure allows the grid/caps to befabricated in many different configurations, e.g., as disk inserts oroverlapping caps. If desired, relief grooves can be machined in thecylinder to ensure appropriate positioning of such a cap or grid.

[0032] Reflectors produced according to the present invention are verylightweight, extremely rugged, and inexpensively and easily massproduced. Additional advantages over the prior art include: greaterdesign flexibility in selecting ring width and spaces; no need tohand-assemble the rings as is required by the prior art; the spacing andwidth of and distance between the rings can be easily controlled byreproducible photo lithographic processing or other appropriateprocessing depending on the material used; lithographic patterns orother patterns produced are scalable for various applications usingsimple computer-aided design techniques; reflectron replacement can beeasily accomplished because of the plug-in nature of the reflectron; anduse of high Tg circuit board material allows operation of the reflectronover wide temperature ranges.

[0033] While the present invention is described herein in connectionwith a TOF mass spectrometer, a reflectron fabricated in accordance withthe present invention can be used in connection with any devicerequiring the creation of electrostatic fields, and particularly indevices requiring precision, rugged, lightweight, inexpensive, modular,and/or mass producible construction. Further, while a cylindricalreflectron is described herein and shown in the drawings, with simplemodifications to the circuit mask, other geometrical shapes, such asconical reflectors, can also be fabricated with high precision.

[0034] While the above-described process uses cured fiberglass layers toprovide the rigid tubular support required for use as an ion reflector,any cured composite material that can be wrapped or rolled around therolled flexible circuit board will suffice. Further, the etched flexiblecircuit board can be formed as a rigid tube using any method whichresults in a rigid tube having the rings formed along the interior ofthe tube. For example, instead of using the fiberglass layers asdescribed above, the etched flexible circuit board could be glued(laminated) to the inside of an appropriate diameter support tube. Thesupport tube could be made of metal or composite materials, dependingupon the required operating conditions. To enable the connector end ofthe flexible circuit board to extend outside of the tube, the tube couldbe provided with a slot that runs almost the entire length of the tube.This slot serves the same purpose as the opening 324 of FIG. 3, i.e., itallows one end of the flexible circuit board to extend through the tubeto permit easy wire attachment or connector attachment to the individualrings formed on the inside of the tube.

[0035]FIG. 5 shows that, if desired, the connector end 104 of flexiblecircuit board 100 can be terminated at a rigid circuit board portion 530as shown. Rigid circuit board portion 530 can accommodate, for example,a voltage divider network 532 (i.e., the precision resistors and theinterconnection pattern necessary to apply a specified voltage to eachof the rings). The incorporation of the voltage divider network 532 ontothe same structure as the ring assembly allows the entire reflectron tobe easily replaced by simply disconnecting the assembly from the twoleads 534 and 536 connecting the voltage divider network to the highvoltage power supply. Configured in this manner, a simple two-pinconnector is all that is required (to make the high voltage power supplyconnection).

[0036] If it is necessary to reduce the weight of the reflectron tubeeven further, as illustrated in FIG. 6, the circuit board 100 may besplit into multiple segments as it exits the reflectron tube and ispassed through multiple slots 640; the multiple slots 640 createintervening slot supports 642, which provide additional rigidity to thestructure while still allowing access to make electrical connections tothe conductive traces 102.

[0037] The foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction andapplications shown and described. Accordingly, all suitablemodifications and equivalents may be resorted to, falling within thescope of the invention and the appended claims and their equivalents.

1. A method of manufacturing a reflectron, comprising the steps of:wrapping a flexible circuit board around a mandrel, leaving a connectorend of said flexible circuit board unwrapped; wrapping one or more pliesof uncured composite material around said circuit board, so that all ofthe exposed portion of said circuit board, except for said unwrappedconnector end, is covered by said composite material ply(s); curing saidcomposite material on said mandrel; and removing said flexible circuitboard and composite material from said mandrel.
 2. A method ofmanufacturing a reflectron as set forth in claim 1, wherein saidcomposite material comprises fiberglass.
 3. A method of manufacturing areflectron as set forth in claim 1, wherein said reflectron forms acircular cylinder.
 4. A method of manufacturing a reflectron as setforth in claim 1, wherein said reflectron forms a rectangular cylinder.5. A method of manufacturing a reflectron, comprising the steps of:photo-etching a plurality of conducting traces onto a flexible substratesheet; wrapping said photo-etched substrate sheet around a mandrel sothat said plural conducting traces coincide to form a plurality of ringssurrounding said mandrel, leaving a connector end of said flexiblesubstrate sheet unwrapped; wrapping one or more plies of uncured,pre-impregnated composite material around said substrate, so that all ofthe exposed portion of said substrate, except for said unwrappedconnector end, is covered by said composite material ply(s); curing saidphoto-etched substrate and composite material on said mandrel; andremoving said cured photo-etched substrate and composite material fromsaid mandrel to form a rigid tubular reflectron.
 6. A method ofmanufacturing a reflectron as set forth in claim 1, wherein saidpre-impregnated composite material comprises fiberglass.
 7. A method ofmanufacturing a reflectron as set forth in claim 1, wherein said rigidtubular reflectron forms a circular cylinder.
 8. A method ofmanufacturing a reflectron as set forth in claim 1, wherein said rigidtubular reflectron forms a rectangular cylinder.